To schedule images using the Bulk Uploader, you’ll need to include an URL (link) to that image on your .csv file. This means that your image must be hosted online and set to public.
In case the images you’re looking into scheduling are stored on your device, you’ll need to use an online service to upload them and get an URL. Keep in mind that the URL should end on an image extension such as .jpg or .png for the Bulk Uploader to correctly process it. Here's an example: https://postcron.com/en/blog/wp-content/uploads/2018/12/artstudio.jpg
If you’re used to services such as Google Drive and Dropbox, you can use them to host your images. Just make sure you set the image's URL to public so Postcron can access its information.
Another way to easily schedule multiple images from your device is by using the Image Uploader. You’ll love it!